Ultrasound transmitted from an ultrasound probe travels while being attenuated in a body, and thus a reflection signal reflected from a deeper region in the body is more likely to be attenuated. To equalize image quality, ultrasound diagnostic apparatuses are capable of previously setting various gains in a depth direction. However, the degree of the attenuation in fact differs among organs and persons, and thus varies for each inspection. Such ultrasound diagnostic apparatuses are capable of adjusting a gain in a time direction, that is, the depth direction. This function is referred to as sensitivity time control (STC) or time gain control (TGC).
Furthermore, image quality in an azimuthal direction may differ depending on how to place the ultrasound probe and a condition in the body of a subject. For example, this causes the left side of an ultrasound image to be dark. Thus, the ultrasound diagnostic apparatuses are capable of adjusting a gain in the azimuthal direction. This function is referred to as lateral gain control (LGC).